Detecting Bird Flu in Humans

Correct, speedy and timely diagnosis of Avian Influenza A(H5N1) virus strain is very important in initiating early treatment of an affected individual.

As the early initiation of treatment after diagnosis is important for the successful recovery of the patient, the correct and professional collection, storage and transportation of specimens is also very crucial.

A good lab certified by WHO or its own regional labs with sophisticated equipment and stringent regulations are necessary for proper diagnosis.

The WHO even requires intimation of transportation to laboratories of specimens of suspected individuals for confirmation tests. The tests can be fast bedside tests or slow but reliable cell culture tests.

Commercial rapid tests for avian influenza depending on immunoassays can give results within half an hour. They look normally for antigens of the influenza virus while others look for neuraminidase activity.

These are also called as bed-side tests; point of care tests and near patient tests. Some experts say their results are unreliable. Confirmatory tests are anyhow inevitable.

The outcome depends as much on the quality and type of specimen used. Nasal aspirates, sputum, nasal washes, nasopharyngeal swabs containing cellular materials are considered superior to nasal and throat swabs.

These tests can recognize both type A and B viruses but unfortunately, not Type A subtypes. These tests must be conducted within 4 to 5 days of onset of illness. In children, the virus shedding is longer up to 5 days.

Rapid tests are useful in the following situations.

• These are helpful in decision making on fast changing cases and to help setup proper clinical setup for patients before confirmatory test results are received.
  
• If confirmed in rapid test stage itself, it allows the doctors to initiate antiviral drugs and prevent nosocomical contaminations.
  
• Useful in communities where outbreaks during season were institutionalized. Rapid testing allows prior control of outbreaks.
  
• Helps diagnose semi-closed communities for outbreaks. They are similarly, also useful for testing air passengers arriving from many destinations.
  
• Whereas, the confirmatory diagnosis gives accurate result, the surveillance need ‘early warning’ of outbreak. Rapid tests fit well here too.

However, there are still situations, where cell culture tests in conjunction with rapid tests are advised.

Virus culture tests are sensitive tests which help identification, antigenic and genetic characterizations, drug susceptibility determination and vaccine preparation.

It preferably uses Madin-Darby Canine Kidney Cells for cell culture and unknown virus are identified by the presence of monoclonal antibodies.

Other techniques used for identification are haemagglutination, antigen analysis for subtypes using haemagglutination inhibition.

Polymerase chain reaction technique is used for virus genome identification. Serological tests for measuring Type A virus specific antigens, involves haemagglutination inhibition test, enzyme immunoassay, virus neutralization test etc. the last test uses live virus for measuring the highly contagious A(H5N1) virus’ antigens, hence restricted to laboratories with Bio-Safety Level-3 facilities.

Care should be taken not to test clinical specimens of birds, animals or humans in the same laboratory for obvious reasons. There are different guidelines available for countries with and without surveillance systems. One may visit the website of WHO, the nodal world body, for guidance.